The present invention relates to mobile terminals and methods and computer program products for operating the same and, more particularly, to audio circuits, methods and computer program products for processing an audio signal of such devices.
A variety of consumer devices, including mobile devices, such as mobile terminals, include both a processor and user input/output devices, such as displays, speakers, microphones and the like. For such devices, the processor is generally configured to process different forms of media content, such as audio files, pictures, animations and the like. For mobile terminals, the processor is also generally configured to process voice and/or video content that may be associated with a phone call voice connection established to the mobile terminal or data connection.
For mobile devices such as mobile terminals, the audio input circuit is typically designed to maximize speech sensitivity and minimize background noise. To some extent, this audio processing for these devices is a function of their physical and electronic design, for example, based on the microphone's frequency response characteristics and the electronic band pass filters in the audio input circuit front end. In addition, a digital signal processor (DSP) is typically included in the mobile terminal that does portions of the audio processing to improve speech clarity and/or to remove extraneous information from a received audio input signal to reduce bandwidth utilization for communication of the audio signal over the wireless network or the like. Processing the input audio signal from a microphone in conventional mobile terminals may include front end bandpass filters to suppress frequencies outside the voice (speech) frequency band, audio compression to maximize sound energy within the voice band and/or a voice activated switch (VOX) that silences (ceases to use) the audio input from the microphone and instead inserts “comfort noise” for over air transmission during a voice call and/or the like.
As used herein, “audio compression” refers to a process that increases the sound energy in the voice/speech band. Audio compression is distinct from “data compression,” which generally removes or encodes redundant information to reduce the amount of information required to represent a voice input and, thereby, to reduce bandwidth requirements for supporting a voice call or the like. For example, replacing pauses with comfort noise, or an indicator that comfort noise is to be inserted in the receiver, is a data compression technique as are standard compression standards, such as MP3.
A conventional audio path as described above is illustrated in the schematic block diagram of FIG. 1. As seen in the illustrative and schematic diagram of FIG. 1, a microphone 12 is coupled to a pre-amplifier 14 that pre-amplifies an analog electrical signal generated by the microphone 12 representative of sound waves detected by the microphone 12. The output of the pre-amplifier 14 is illustrated coupled to a bandpass filter 16 that is configured to pass only signals in the voice frequency band to thereby remove extraneous noise and the like which may otherwise interfere with the quality of the recordation (detection) of speech received by the microphone 12. The output of the bandpass filter 16 is passed to an analog to digital converter (ADC) 18 and the digitized filtered audio signal is then processed by a digital signal processor (DSP) 20. As noted above, the digital signal processor 20 may be configured to provide further filtering, audio compression, comfort noise insertion and/or the like. The DSP 20 may also do standardized formatting for the audio signal to place it in a standardized digital form such as pulse code modulation (PCM).